The thornier the problem the older the heads you need to solve it. So classical saws would have you believe. And so did the managers of the Shugborough estate when they sought the help of two Bletchley Park veterans to decipher a 250-year-old cryptic inscription reputedly telling the whereabouts of the Holy Grail. Only the experts weren't able to interpret the jumble of letters, despite carrying with them an original Enigma decoding machine. Was it because they didn't know enough ancient Greek? Or was it because it was a joke in the first place? "It remains an enigma," says Shugborough's manager. Quite so. It's the fault of the machine then.